PEORIA — A fire that damaged a West Bluff apartment building severely enough Tuesday morning to require an emergency demolition order likely resulted from the same electrical incident that sparked a less serious fire one day earlier.

Fire investigators will never know with 100 percent certainty that the blaze at 109 NE Roanoke Ave. was electrical in nature because the extent of damage has made entry into the structure and further on-site investigation unsafe, arson investigator Brad Pierson said at a news conference Wednesday.

But the flames that erupted in the attic of the 12-unit apartment complex shortly before 8 a.m. Tuesday probably smoldered undetected for more than a dozen hours in several inches of cellulose insulation on the other side of a firewall from where firefighters extinguished a less intense blaze Monday afternoon.

The cellulose insulation in particular masked the heat signature of the smoldering flames from firefighters’ thermal cameras on Monday afternoon, Pierson said.

“There was no presence of fire to the best they could tell at that time,” he said.

Ameren Illinois cut electricity and natural gas service to the building following the blaze Monday afternoon, which caused an estimated $20,000 in damage and originated in a different section of the attic. An adjacent apartment building at 107 NE Roanoke Ave. also had power cut as a precautionary measure after the Tuesday fire. Residents will be allowed to return to that property once electricity is safely restored.

Eight of the 12 units at 109 NE Roanoke were occupied until the Monday afternoon fire. The building was vacant at the time of the Tuesday morning fire. A date for demolition has not yet been scheduled, but the building will be torn down once contractors secure necessary equipment.

Some of the unoccupied apartments were under repair from a fire in the apartment building about a year ago, Pierson said. The owner of the property, Roger Heim, had worked with the Peoria Fire Department after the blaze a year ago to bring the affected units up to code.

Matt Buedel can be reached at 686-3154 or mbuedel@pjstar.com. Follow him on Twitter @JournoBuedel.